1. Field
The present invention generally relates to the field of wireless communication systems, and more specifically to techniques using antenna polarization in wireless communication system.
2. Background
In wireless communication systems several users share a common communication channel. To avoid interference arising from several users transmitting information over the communication channel at the same time, some form of allocation of the available channel is required. Allocation of user access to the communication channel can be achieved by various forms of multiple access protocols, such as code division multiple access (CDMA). In CDMA systems, also referred to as “spread spectrum” systems, each signal is separated from those of other users by coding the signal. Each user uniquely encodes its information signal into a transmission signal. The intended receiver, knowing the code sequences of the user, can decode the transmission signal to receive the information.
A technique for increasing the signal to interference ratio, analogous to what is utilized in FDMA (“Frequency Division Multiple Access”) wireless communication systems, is to use different frequencies in different cells, or even in different sectors within a cell in order to increase signal to interference ratio. For example, a cell can be divided into three sectors, each assigned a different frequency. The same frequencies can be similarly allocated in other cells in the system, which is known as frequency reuse. Where adjacent sectors are allocated different frequencies the interference between their signals is reduced, and the signal to interference ratio for users in the two adjacent sectors is increased. Therefore, the sectors' capacity is increased with frequency reuse, but the disadvantage is that frequency reuse necessitates using more frequencies.
It would be desirable to further increase signal to interference ratios in wireless communication systems as a means to enhance and complement the presently known approaches of using different frequencies to increase signal to interference ratio at a receiver terminal. It is also further desirable to achieve an increased signal to interference ratio at the receiver terminal without expending a large amount of system bandwidth.